Yoghurt, pudding, butter, and other semiliquid materials, typically dairy-type foodstuffs, are normally packaged in a cup having a circular upper edge that is sealed to the periphery of a circular foil cover disk. The filling and sealing are done under substantially sterile conditions so that the hermetically packed material will not spoil unless opened. Such a package can be made at very low cost yet can provide a sealed sterile containment for the foodstuff.
The apparatus for producing such a package normally includes a picker device that pulls the cups from a supply and fits them to seats at the extreme upstream end of the upper stretch of a conveyor belt or chain. The cups pass through a device that picks out doubled cups and fills in where cups are missing, then they pass through an apparatus that sterilizes them with hydrogen peroxide or the like. Subsequently the cups are filled downstream of the sterilizer by a machine which deposits the product into each cup. Cover disks are set atop the filled and sterilized cups and the covers are sealed to the rims of these cups. The seal of each cup and cover is then tested and finally an unloader takes the packages off the conveyor chain, automatically culling out those packages found to have imperfect seals.
The sterilizing device normally sprays each cup and even the cover with a msit of dydrogen peroxide. Although only a small amount of this sterilizing liquid is needed with each cycle of the step-wise operating machine, it is essential that the amount used be very accurately dosed. If too little sterilizing liquid is used the product in the unsterile package will spoil; if too much is used the product will be flooded and diluted. Either way the product will be ruined.
Accordingly the standard procedure is to use a dosing device comprising a sight-glass reservior into which the sterilizing liquid is fed by a continuously operating light-duty pump whose intake is connected to a supply filled with the liquid. A riser tube has an upper end fixed at a location above the base of the reservoir and is connected to the liquid supply, which itself is at a lower level. Thus the liquid level in the reservoir is always level with the rim of the riser tube as any excess liquid will drain out through the riser tube.
The spray nozzle has an input connected to a cup that is dipped with each cycle into the reservoir. Since the reservoir's level remains substantially unchanged, such a procedure will always dip out an exactly equal quantity of the sterilizing liquid which is then aspirated by a tube connected to the spray nozzle of the sterilizer, which typically works in the manner of a jet-pump aerosol, that is with a jet of gas operating over a venturi connected to the intake tube. Thus with each cycle or step of the machine the doser, whose pump is going continuously, must dip out and then aspirate a small quantity of the sterilizing liquid. If this is attempted too quickly the resultant splashing and spilling will cause loss of some of the ladled-up liquid and generally irregular dosing.
In order to verify that the system is working properly a monitoring apparatus is connected to the intake tube of the nozzle and normally also to the cup it draws from, these two elements being electrically isolated so that there is only a low-resistance path between them when the sterilizing liquid contacts and bridges them. Under normal circumstances at the start of an aspiration cycle, which takes place intermittently like most functions of the packaging machine, the liquid bridges the intake tube and cup and creates a very low-resistance path betwen them. On the contrary at the end of the intake cycle, when the liquid in the dip cup is depleted, the resistance is high because the liquid has been sucked out of this cup and the dip tube is separated by an air space from the cup. Such a device is sold under the tradename "Level Device GVD" by the firm of Helmut Negele (Hauptstrasse 14,D-8941 Egg a.d. Gunz, West Germany). Thus if the feed pump is not working, the cup will not be filled at the start of the cycle and this device can shut down the line, and if the intake line to the nozzle or the nozzle is clogged and the liquid is not sucked out of the cup by the end of the cycle, the system is similarly shut down.
Such a system is fairly complicated. The various reciprocating parts are subject to considerable wear. In addition resetting it to dose a greater or smaller quantity of the liquid is complex because, as mentioned above, faster operation involves loss of efficiency and liquid with each operation.